This invention relates to stern drive systems for boats and ships, and in particular to an improved stern drive system that is easier to install and less expensive to manufacture and maintain.
Stern drive systems commonly in use include a first propulsion element that is supported outside of a hull of a boat or ship, a second propulsion element, and a pivot joint that interconnects the first and second propulsion elements. If the stern drive is a jet drive, the second propulsion element will typically be a jet nozzle. If the stern drive is a propeller drive the second propulsion element will include a propeller. Typically, multiple actuators are coupled to the second propulsion element to steer the second propulsion element in two planes: a horizontal steering plane, which is used to steer left and right, and a vertical trim plane, which is used to change the vertical direction of thrust and thereby to trim the boat.
One widely used stern drive is sold under the trade name ARNESEN. This drive uses triangulated hydraulic cylinders to prevent the second propulsion element from rotating about an axis defined by the first propulsion element. With this approach opposed hydraulic cylinders maintain the second propulsion element pointed in the desired direction.
This approach brings with it several disadvantages. First, because the hydraulic cylinders work in opposition to one another, if they are not properly balanced the cylinders are subjected to increased wear, which results in reduced life and consequently increased maintenance cost. Second, this stern drive can be difficult to install. Installation is relatively expensive, and it often requires especially trained technicians to obtain the desired alignment. Furthermore, the installation is physically large, which may limit the application in some cases.